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Septic on a Canyon Lake Lot: The Flowage Easement and Setbacks

Around Canyon Lake, the question of where a septic system can go starts with the US Army Corps of Engineers, not the county. Here is how the Corps flowage easement, the Comal County order and the TCEQ setback table fit together on a lake lot.

Three lines around the lake

The Corps' Canyon Lake leaflet, Know Your Boundaries, describes three zones. The federal government owns the land under the lake at the conservation pool elevation of 909 ft above mean sea level, plus a strip of varying width around it, marked by concrete monuments with brass caps. No private building or exclusive use is allowed there.

Above that, the government holds perpetual flowage easements over certain private land, giving it the right to flood that land in operating the lake. These are generally the private lands below the 948 ft contour. Not every property has one, and the line is often a metes and bounds description rather than the contour itself, so the deed history decides. The leaflet also warns that an easement still applies even if a newer deed leaves it out.

Above the easement is private land under the normal county rules.

What the Corps says about septic systems

The flowage easement generally lets the government prevent human habitation on it. Building any structure, including utility lines, wells and fill, needs the District Engineer's written approval first. For water wells, sewer lines and septic systems, the leaflet says each case is examined to make sure the lake will not be polluted or the reservoir disrupted, and that any septic installation must first be approved by the city, county or state health department.

It is also blunt about two numbers. It says state law requires septic installations to sit at least 75 ft, measured horizontally and upslope, from the 50-year floodplain at the 940 ft contour. And it says the Corps will not allow septic tanks below elevation 948.

The county asks for the Corps first

Section 10.11 of the Comal County septic order says that if any part of the system is proposed in a Corps flowage easement, you need Corps approval before applying to the county for a permit. Section 10.5 adds a floodplain check by the County Flood Plain Administrator. Our county rules page lists the other local requirements.

The sensible order on a lake lot is survey, then deed and easement check, then the Corps conversation if the system might reach below 948, then the site evaluation and the county permit.

TCEQ distances from the lake

TCEQ's separation table, 30 TAC §285.91(10) Table X, sets distances from streams, ponds, lakes and rivers:

• Septic or treatment tank: 50 ft.
• Soil absorption field: 75 ft.
• Spray area: 75 ft, or 50 ft with secondary treatment and disinfection.
• Drip irrigation: 25 or 75 ft, depending on the soil's rating.

Slopes where seeps may occur carry their own distances too, and lake lots often have them. In Comal County the spray area also stays at least 20 ft from every property line, with no reduction for a timer.

Wells and lake water on the same lot

Many lake homes draw water as well as discharge it, and the two have to be kept apart. Table X puts a private well 50 ft from a tank and 100 ft from an absorption field or spray area. Drawing from the lake itself takes a Corps license to run an intake line across government land, and the leaflet says you need water rights from the Guadalupe-Blanco River Authority before you apply. Pumps and electrical parts must stay off federal property, and submersible pumps for private domestic use are prohibited at Fort Worth District lakes.

Check the contributing zone map

Comal County is one of the counties named in TCEQ's Edwards Aquifer contributing zone rules, 30 TAC Chapter 213, Subchapter B. Those rules apply to regulated activities that disturb five acres or more, or less as part of a larger common plan of development. Where a Contributing Zone Plan is required, the county will not issue an authorization to construct until TCEQ has approved it. The county's environmental health page links to its contributing zone map, so check the lot there. The recharge zone rules are on our Edwards Aquifer page.

Questions people ask

Can a septic tank go below 948 ft at Canyon Lake?

The Corps' Canyon Lake leaflet says it will not allow septic tanks below elevation 948.

How do I know if my lot has a flowage easement?

Check the deed history, since the easement is often a metes and bounds line rather than the 948 contour. The Corps Canyon Lake Project Office, 830-964-3341, can schedule a field appointment.

Who issues the septic permit for a Canyon Lake home?

Comal County Environmental Health, 195 David Jonas Drive, New Braunfels, (830) 608-2090. If any part of the system would be in a Corps flowage easement, get Corps approval first.